Steam Power Plant Reheat Efficiency Calculation

In Summary,-The label in the schematic diagram that was given to us was wrong. I adjusted my TS diagram based on the correction and tried to solve it again.-Thankfully I got the answers now.
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Homework Statement


vuKJEna.png


Homework Equations


Heat added, Qa (This I'm not sure how since the steam passed through a reheater before it enters the HPT. That is what I understand based on the problem above)
Work Net, Wnet
Efficiency, Wnet/Qa
Heat Rate, WP/EP (Not sure if that is the correct formula)

The Attempt at a Solution


First I made a T-S Diagram
w4NX6Ax.jpg


Based on the diagram above, I got all these enthalpy values.
OZzSVlg.png

h1 = h @ 3 MPa & 370C
h2 = h @ 0.7 MPa & s1
h3 = h @ 0.7 MPa & 500C
h4 = hf4 +x hfg4 (All values, 0.007 MPa)
where x = (s4 - sf4)/sfg4
h5 = hf @ 0.007 MPa
h6 = vf5 (P6-P5)
WP1 = h6-h5
ha = h @ 3 MPa and 500C

The WNet that I got is, 1485.491
For the Qa = (ha-h6) + (h3-h2) = 3959.022

Eff = .3752

Was not able to solve Heat Rate.

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I can't seem to understand how the answers shown in the problem was got. Please enlighten me. Thanks in advance!
 
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  • #2
It looks to me like h3 is wrong. It should be equal to h2 plus the heat given up by the high pressure stream between 500 C and 370 C. So, it should be about 3100 J/kg.
 
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Thank you for your reply.
Should I get the heat given up by using this formula?
Q=mcT
 
  • #4
Sent said:
Thank you for your reply.
Should I get the heat given up by using this formula?
Q=mcT
Sure. Or you can get it from the steam tables as the ##\Delta h##. Both should give about the same answer.
 
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Chestermiller said:
Sure. Or you can get it from the steam tables as the ##\Delta h##. Both should give about the same answer.
Hello,

We was informed that the label in the schematic diagram that was given to us was wrong. I adjusted my TS diagram based on the correction and tried to solve it again. Thankfully I got the answers now.

Thank you very much for your replies.
 

1. What is a reheat cycle in a steam power plant?

A reheat cycle in a steam power plant is a process where the steam is sent back to the boiler after partial expansion in the turbine. The steam is then reheated and sent back to the turbine for further expansion, increasing the efficiency of the power plant.

2. How does a reheat cycle improve the efficiency of a steam power plant?

A reheat cycle improves the efficiency of a steam power plant by reducing the moisture content in the steam and increasing the average temperature of the steam. This results in more work being done by the turbine and therefore, more electricity being generated.

3. What are the components of a reheat cycle in a steam power plant?

The components of a reheat cycle in a steam power plant include a high-pressure turbine, a reheater, a low-pressure turbine, and a condenser. The high-pressure turbine expands the steam, which is then sent to the reheater where it is reheated before entering the low-pressure turbine. The condenser then converts the steam back into water for reuse in the boiler.

4. What are the advantages of using a reheat cycle in a steam power plant?

Some advantages of using a reheat cycle in a steam power plant include increased efficiency, reduced moisture content in the steam, and improved turbine performance. Additionally, a reheat cycle allows for better control of the temperature and pressure of the steam, which can help prevent damage to the turbine.

5. What are the limitations of a reheat cycle in a steam power plant?

One limitation of a reheat cycle in a steam power plant is the increased cost of installation and maintenance. The additional components required for the reheat cycle add to the overall cost of the power plant. Additionally, a reheat cycle may not be suitable for smaller power plants as the benefits may not outweigh the added cost.

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